RATIONALE: Drugs used in chemotherapy, such as cytarabine and clofarabine, work in different ways to stop the growth of cancer cells, either by killing the cells or by stopping them from dividing. Giving more than one drug (combination chemotherapy) may kill more cancer cells. PURPOSE: This phase II trial is studying how well giving cytarabine together with clofarabine works in treating patients with relapsed or refractory acute lymphoblastic leukemia.

Primary objective: * Determine whether the complete remission rate in adult patients with relapsed or refractory acute lymphoblastic leukemia (ALL) is sufficiently high after treatment with cytarabine and clofarabine to warrant further investigation. Secondary objectives: * Estimate the frequency and severity of toxicities associated with this dosing schedule of cytarabine and clofarabine. * Investigate, preliminarily, the prognostic effects of cytogenetic features on response to treatment in these patients. Other objectives (if funding allows): * Investigate, preliminarily, the prognostic effects of laboratory correlates (expression of nucleoside transporters, expression of other pertinent genes by tissue microarray) and FISH features on response to treatment in these patients OUTLINE: This is an open-label, multicenter study. * Induction therapy (1 or 2 courses): Patients receive induction therapy comprising clofarabine IV over 1 hour followed 4 hours later by cytarabine IV over 2 hours on days 1-5 (course 1). Patients who achieve a response (5-25% blasts in the bone marrow with a ≥ 50% reduction in blasts from initial bone marrow aspirate) receive 1 more course of induction therapy beginning no later than day 45. Patients who achieve complete remission (\< 5% blasts in the bone marrow) after 1 or 2 courses of induction therapy may proceed to consolidation therapy. * Consolidation therapy (1 course): Beginning within 60 days after the first day of the last induction therapy, patients may receive consolidation therapy comprising clofarabine IV over 1 hour followed 4 hours later by cytarabine IV over 2 hours on days 1-4. After completion of study treatment, patients are followed periodically for up to 5 years. PROJECTED ACCRUAL: A total of 35 patients will be accrued for this study.